1. Field of the Invention
The present invention relates to a technology for suppressing a leakage current at the time of image acquisition in a display device including an image acquisition function or in an image acquisition circuit.
2. Description of the Related Art
A liquid crystal display device includes: a pixel array part including pixels at respective portions where a plurality of signal lines and a plurality of scan lines intersect with each other; and drive circuits which drive the signal lines and the scan lines. Along with the recent advanced development of integrated circuit technologies, a process technology for forming a part of the drive circuits on an array substrate together with the pixel array part has been put to practical use. Accordingly, the whole liquid crystal display device can be reduced in weight and size. Consequently, the liquid crystal display device is widely used as a display unit for various portable devices such as a portable telephone and a laptop computer.
Incidentally, herein proposed is a display device in which a contact-type area sensor performing image acquisition is disposed on an array substrate. For this technology, for example, Japanese Patent Laid-Open No. 2001-292276 and Japanese Patent Laid-Open No. 2001-339640 are disclosed.
Polysilicon has a larger mobility of electrons than that of amorphous silicon and therefore it is preferable to use polysilicon in order to form a part of the drive circuits on an array substrate.
However, even if active layers of various TFTs (thin film transistors) formed on the array substrate are formed of polysilicon, when a number of dangling bonds exist in the active layers, there is a problem of a leakage current flowing into the TFTs.
For solving such a problem, a technique of hydrogenating the active layers and terminating the dangling bonds is considered. However, in the case of the above-described contact-type area sensor, there is a problem in that, when the dangling bonds in the active layers are terminated, sensitivity to light is lowered.
Moreover, in an optical sensor diode used in a conventional image acquisition circuit, even if a reverse bias voltage is 0V, a weak leakage current is generated when light is irradiated, thus causing the accuracy of image acquisition deteriorate.